Process and apparatus for multi-fuel operation of an air-compressing and auto-igniting injection internal combustion engine

ABSTRACT

A method and apparatus for the operation of an air-compressing and auto-igniting injection-type internal combustion engine for multi-fuel operation in which a flame-suction-air heater, known as such, for cold-starting operation is started during the operation of the engine under load with poorly ignitable fuels such as gasoline; the engine is thereby of the type which has a relatively low compression ratio for self-igniting fuel operation.

United States Patent Hardenberg et al.

1451 Feb. 26, 1974 PROCESS AND APPARATUS FOR MULTI-FUEL OPERATION OF ANAIR-COMPRESSING AND AUTO-IGNITING INJECTION INTERNAL COMBUSTION ENGINEInventors: Horst Hardenberg, Stuttgart;

Gerhard F r'zinkle, Grunbach, both of Germany Daimler-BenzAktiengesellschaft, Stuttgart-Unterturkheim, Germany Filed: Mar. 27,1972 Appl. No.: 238,336

Assignee:

Foreign Application Priority Data Mar. 27, 1971 Germany 2115001 us. on123/122 D, 123/122 0, 123/179 1-1, 123/179 L Int. Cl. o2m 31/04,1=02n17/09 Field of Search "12371791111791; 179 R,

122 D, 123/122 G, 142.5, 180 R References Cited UNITED STATES PATENTS6/1936 Woolson 123/179 H 3,020,903 2/1962 Kloss 123/1425 R 3,024,7773/1962 Baker.... 123/122 G 3,335,710 8/1967 Reddy... 123/179 L X3,353,520 11/1967 Haag 123/122 D X 3,450,109 6/1969 Gratzmuller..123/122 D X 3,534,723 10/1970 Tramontini 123/1425 R X 3,656,465 4/1972Frankle 123/179 H 3,687,122 8/1972 Kamo 123/122 G Primary Examiner-AlLawrence Smith Attorney, Agent, or Firm-Craig and Antonelli [57]ABSTRACT A method and apparatus for the operation of an aircompressingand auto-igniting injection-type internal combustion engine formulti-fuel operation in which a flame-suction-air heater, known as such,for coldstarting operation is started during the operation of the engineunder load with poorly ignitable fuels such as gasoline; the engine isthereby of the type which has a relatively low compression ratio forself-igniting fuel operation.

38 Claims, 3 Drawing Figures PROCESS AND APPARATUS FOR MULTI-FUELOPERATION OF AN AIR-COMPRESSING AND AUTO-IGNITING INJECTION INTERNALCOMBUSTION ENGINE The present invention relates to a process for theoperation of an air-compressing and auto-igniting injection internalcombustion engine for multi-fuel operation and an internal combustionengine operating according to this process. During the ooperation with apoorly ignitable fuel, such as, for example, gasoline, it often involvesdifficulty to attain a completely satisfactory selfor auto-ignition andto maintain a satisfactory operation under load.

It is known for avoiding these difficulties to preheat the suction airwith the aid of a heat-exchanger, through which flows the cooling water,or also to add heat thereto by the admixture of exhaust gases. Bothprior art solutions do not satisfy in numerous cases. An upper limit isimposed to the heating by means of a cooling water heat-exchanger by thecooling water temperature, and exhaust gases in the suction air reducethe oxygen content of the combustion air.

The present invention is concerned with the task to achieve a safeauto-ignition under load operation by simple means also in case of verypoorly ignitable fuels, in internal combustion engines with a relativelylow compression ratio (and corresponding low mechanical load) or underotherwise unfavorable operating conditions. The underlying problems aresolved in accordance with the present invention in that especially inengines with a compression ratio which is relatively low forself-igniting multi-fuel operation, preferably with a compression ratioas utilized with customary Diesel engines during the operation underload conditions with poorly ignitable fuels, for example, gasoline, aflame-suction-air heater known as such for coldstarting operations isset into operation. It is assured in this manner that a temperature isalways present in the combustion space which is sufficient for an autoignition.

It simplifies the construction of the installation and the operation ifthe same fuel is utilized for the operation of the flame suction heateras for the operation of the internal combustion engine.

In most cases under certain operating conditions, the assist of theflame-suction air heater will not be necessary. The fuel requiredtherefor would be consumed needlessly and even harmful consequences suchas, for example, material damages or reduction in power output by reasonof excessively hot suction air might occur. For these reasons, it isproposed in an embodiment of the present invention that theflame-suction-air heater upon reaching a temperature sufficient for anignition without the preheating by the flame-suction air heater in thecombustion space is automatically turned off. This can take place by amechanism which turns off the flame-suction air heater in dependence onthe fuel quantity injected into the internal combustion engine, forexample, in dependence on the position of the control rack of theinjection pump. The turning-off, however, may also take place, forexample, in dependence on the exhaust gas temperature. (Fuel quantity asalso exhaust gas temperature provide a measure for the temperature inthe combustion space which is the really important factor).

It may be advantageous under certain circumstances to cause theturning-off additionally in dependence on the rotational speed becausethe rotational speed also influences the auto-ignition behavior: At verylow rotational speeds, the compression end temperature drops because alonger period of time is available, considered from an absolute point ofview, for the cooling by means of the cooling water or the cooling air;and at high rotational speeds, the ignition delay must become shorter,calculated in absolute values because otherwise the coordination of theactual ignition to the piston position would no longer be correct. Onehas to take care by the use of warmer suction air that the ignitiondelay is shortened. If one therefore makes the shutting-off of theflame-suctionair heater additionally dependent on the rotational speed,one shuts off the flame-suction air heater at every rotational speedprecisely when, with a view to a completely satisfactory continuedrunning of the engine, it becomes possible in the non-assistedauto-ignition operation; in others words: One does not need to buildinto the automatic control mechanism a safety factor because of therotational speed fluctuations.

Furthermore, a system is proposed in an embodiment of the presentinvention which measures auxiliary magnitudes such as, for example, thedensity or specific weight, which serve as a measure for theignitability of the internal combustion engine fuel, and whichestablishes the operating readiness of the flame-suction-air heatingsystem only in case of poorly ignitable fuels. The significance of thismeasure becomes apparent at once, for only with poorly ignitableinternal combustion engine fuels, the flame-suction-air heater isrequired under load operation. However, one can also utilize theflame-suction-air heater with appropriate controls of any conventionaltype for the starting, and more particularly possibly also withotherwise ignitable internal combustion engine fuels.

Finally, it may be advantageous if heat-insulating measures for theprevention of the heat flow from the piston top surface on thecombustion space side to the piston running surface are provided at thepiston, for example, by the provision of a heat insulating groove. Thepiston top surface then remains hotter, and one is able to get alongwith less fuel for the flame-suction-air heater or one is able to shutoff the heater earlier.

Accordingly, it is an object of the present invention to provide aprocess and apparatus for the operation of an air-compressing,auto-igniting injection internal combustion engine for multi-fueloperation which avoids by simple means the aforementioned shortcom ingsand drawbacks encountered in the prior art.

Another object of the present invention resides in a method andapparatus for operating an aircompressing, auto-igniting internalcombustion engine for multi-fuel operation which maintains a completelysatisfactory operation and a completely satisfactory self-ignition underall load and operating conditions.

A further object of the present invention resides in an internalcombustion engine of the type described above which assures a reliableauto-ignition under load even with the use of poorly ignitable fuels,with relatively low compression ratios and under otherwise unfavorableoperating conditions.

A still further object of the present invention resides in a method andapparatus for operating an aircompressing autoingiting internalcombustion engine of the injection type for multi-fuel operation whichassures at all times an adequate temperature in the combustion space forthe auto-ignition by an appropriate control of a flame-suction-airheater.

Another object of the present invention resides in a process andapparatus for operating a multi-fuel internal combustion engine of thetype described above which permits efficient use of a flame-suction-airheater without the danger of damage to the engine or parts thereof or areduction in the output of the engine due to excessively hot suctionair.

These and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in connection with the accompanying drawing which shows, forpurposes of illustration only, one embodiment in accordance with thepresent invention, and wherein:

FIG. 1 is a schematic side view of an internal combustion engineoperating according to the method in accordance with the presentinvention;

FIG. 2 is a partial axial cross-sectional view through the piston toppart with a heat-insulating groove in accordance with the presentinvention; and

FIG. 3 is a diagram indicating operating magnitudes which have aninfluence on the behavior of the autoingition. I

Referring now to the drawing, and more particularly to FIG. 1, theinternal combustion engine generally designated by reference numeral 1illustrated in this figure is constructed as air-compressing andautoigniting injection internal combustion engine which has acompression ratio that is relatively low for autoigniting multi-fueloperation. Fuel is metered to the individual cylinders of the internalcombustion engine l by an injection pump 2, to which this fuel is fed byway of a line 4 coming from a fuel tank 3.. The air required for thecombustion of the fuel in the combustion spaces of the cylinders issupplied to the suction line 6 by means of a super-charger 5 which maypossibly be constructed as exhaust gas turbo-charger; the combustion airreaches the cylinders from the intake manifold 6 by way of individualsuctionpipe connections.

In order to be able to operate the internal combustion engine ll underload with poorly ignitable fuels, for example, with gasoline, andthereby to achieve a favorable ignition and running behavior, aflame-suction-air heater 7 is provided at the beginning of the suctionline or intake manifold 6, by means of which a flame heating of thesuction air is produced in the suction line 6 by the combustion of thesame type of fuel as is also used for the operation of the internalcombustion engine. The flame-suction-air heater 7 which may be of anyconventional construction is equipped with an injection device for thefuel consisting of a pump and of a discharge nozzle and with an ignitiondevice. Additionally, shields or the like are arranged in the suctionline 6 which prevent a blowing out of the produced flame and whichcontribute to achieving an intimate mixing between air and fuel. Fuel isfed to the flamesuction-air heater 7 by way of a pipe line 8 whichbranches off from the pipe line 4.

For the control of the flame-suction-air heater 7, an installation 9 isprovided which controls the beginning and the end of the preheating ofthe suction air, the fuel quantity to be injected and the ignitionsystem. This control installation 9 which is of conventionalconstruction and forms no part of the present invention is,

in its turn, influenced by a device 10 connected in the pipe line 4 andby a device 11 arranged at the injection pump 2.

The device 10 measures by conventional means the specific weight of thefuel as characteristic for the type of the fuel which is supplied at anygiven time in the pipe line 4 leading to the injection pump 2 andattains combustion in the internal combustion engine, whereas the device11 indicates to the installation 9 by conventional means also, therespective position of the control rack in the injection pump 2. Sincedevices as are used for the measuring device 10 and displacement pick-uplll are known in the art, a detailed description thereof is dispensedwith herein.

The flame-suction-air heater 7 operates automatically in such a mannerthat during the operation of the internal combustion engine l with fuelthat is not poorly ignitable, for example, with Diesel oil, nopreheating of the suction air takes place whereas when the device 10measures a feed to the injection pump 2 of a poorly ignitable fuel, forexample, of gasoline, the flame-suction-air heater 7 is set immediatelyinto operating readiness. The actual operation is maintained with theaid of the device ll for such length of time until the internalcombustion engine operates in a load range in which also poorlyignitable fuels are combusted without difficulties and troubles.

The installation may also be so constructed that the flame-suction-airheater starts to operate independently of the type of the fuel suppliedto the internal combustion engine at low outside temperatures forfacilitating the starting operation and remains in operation after thetermination of the starting operation only if poorly ignitable fuelsflow through the pipe line 4.

The control installation 9 may also be operatively connected tocombustion space temperature measuring device 18 and/or exhaust gastemperature measuring device 19 such that the heater 7 is shut off whenthe effective combustion space temperature is sufficient to supportignition of even poorly ignitable fuels (the combustion spacetemperature being either measured directly by device 18 or indirectly bydevice 19). If either of devices 18 or 19 are utilized, the device 11need not necessarily also be connected.

The piston 12 according to FIG. 2 of the internal combustion engineillustrated in FIG. 1 is provided with a heat-insulating groove 13 whichsurrounds the combustion space recess 14 and which prevents a flowingoffof heat from the combustion space recess 14 in the direction toward thesliding surfaces of the piston. As a result of the construction of thepiston 12 with the heat-insulating groove 13 and the higher pistontemperature conditioned thereby, one is able to keep the fuelconsumption of the flame-suction-air heater 7 (FIG. 1) lower.Additionally, the flame-suction-air heater can be shut off earlier.

The diagram according to F IG. 3 illustrates the effective averagepressure in the internal combustion engine 1 (FIG. 1) as a function ofthe rotational speed of the internal combustion engine whereby thecurves 15 and 16 represent the effective average pressure atrespectively constant injection quantity, and more particularly, thecurve 15 at full load and the curve 16 at a predetermined partial load.The curve 17 represents the average pressure, below which anauto-ignition operation at the respective rotational speed is no longerpossible without setting into operation the flame-suctionair heater.

If one therefore makes the shutting-off of the flamesuction-air heaterdependent exclusively on the average pressure (position of the injectionpump control rack), then one can shut off the flame-suction-air heateronly upon reaching the control rack position of the curve 16 andtherefore has to keep the system in operation superfluously within thearea between the curves 16 and 17. An additional correction as afunction of the rotational speed, (by schematically indicated enginerotational speed measuring device however, would make it possible torealize the shut-off control along the curve 17 which would then takeplace at the individual rotational speeds with differing control rackposition. Since means for detecting the rotational speed are known assuch, a detailed description thereof is also dispensed with herein.

While we have shown and described only one embodiment in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous changes and modifications asknown to those skilled in the art, and we therefore do not wish to belimited to the details shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

What we claim is:

1. A method of operating an air-compressing and auto-igniting injectioninternal combustion engine with multiple fuel operating capabilitycomprising:

providing a selectively operable flame-suction-air heater means forselectively heating intake air supplied to the engine,

and controlling the operation of said heater means with control means,

wherein said controlling includes measuring auxiliary magnitudes whichindicate the ignitability of fuel being supplied to the engine andoperating said heater means during at least some engine operatingconditions only when relatively poorly ignitable fuel is being suppliedto the engine.

2. A method according to claim 1, characterized in that the poorlyignitable fuel is gasoline.

3. A method according to claim 2, characterized in that the internalcombustion engine has a relatively low compression ratio.

4. A method according to claim 1, comprising the step of using the samefuel for the operation of the heater means as is used for the operationof the internal combustion engine.

5. A method according to claim 4, further comprising the step ofautomatically shutting off the heater means upon reaching a temperaturein the combustion space of the engine sufficient for an ignition withoutpreheating by the heater means.

6. A method according to claim 1, further comprising the step ofautomatically shutting off the heater means upon reaching a temperaturein the combustion space of the engine sufficient for an ignition withoutpreheating by the heater means.

7. A method according to claim 6, wherein said step of automaticallyshutting off the heater means includes detecting the quantity of fuelbeing supplied to the engme.

8. A method according to claim 6, wherein said step of automaticallyshutting off the heater means includes detecting the engine exhaust gastemperature.

9. A method according to claim 1, wherein said controlling includesoperation of said heater means independently of the fuel being suppliedto the engine dur ing engine starting operations at low outsidetemperatures and maintaining operation of said heater means after saidengine starting operations only when said relatively poorly ignitablefuel is being supplied to the engine.

10. A method according to claim 9, further comprising the step ofautomatically shutting off the heater means upon reaching a temperaturein the combustion space of the engine sufficient for an ignition withoutpreheating by the heater means.

11. A method according to claim 1, wherein said measuring includesmeasuring the specific gravity of the fuel.

12. A method according to claim 1, further comprising the step ofautomatically shutting off the heater means in dependence on the enginerotational speed.

13. An internal combustion engine for multi-fuel operation comprising:

heater means for heating intake air being supplied to the engine,

and heater control means for automatically controlling the operation ofsaid heater means,

wherein said control means incldes fuel characteristic measuring meansfor measuring auxiliary magnitudes which indicate the ignitability offuel being supplied to the engine and means for maintaining operation ofsaid heater means during at least some engine operating conditions onlywhen relatively poorly ignitable fuel is detected by said fuelcharacteristic measuring means.

14. An internal combustion engine according to claim 13, wherein saidcontrol means includes means for operating said heater meansindependently of the ignitability of the fuel being supplied to theengine during engine starting operations at low outside temperatures andmeans for maintaining operation of said heater means after thetermination of engine starting operations only when said relativelypoorly ignitable fuel is being supplied to the engine.

15. An internal combustion engine according to claim 13, wherein saidengine is an air-compreswing, injection-type engine with auto-ignition.

16. An internal combustion engine according to claim 15 characterized inthat the engine has a relatively low compression ratio for auto-ignitingmulti-fuel operation.

17. An internal combustion engine according to claim 15, characterizedin that the compression ratio of the engine is of the order of thecompression ratio utilized in customary Diesel engines.

18. An internal combustion engine according to claim 17, characterizedin that the fuel which is poorly ignitable is gasoline.

19. An internal combustion engine according to claim 15, characterizedby means for supplying the same fuel for the operation of the heatermeans as is used for the operation of the internal combustion engine.

20. An internal combustion engine according to claim 15, characterizedby further means for shutting off the heater means upon reaching atemperature in the combustion space of the internal combustion enginewhich is sufficient for an ignition without preheating by the heatermeans.

i 21. An internal combustion engine according to claim 20, wherein saidfurther means shuts off the heater means as a function of the quantityof fuel injected into the internal combustion engine.

22. An internal combustion engine with an injection pump having acontrol rack according to claim 21, characterized in that said furthermeans is operable as a function of the position of the control rack ofthe injection pump.

23. An internal combustion engine according to claim 20, characterizedin that said further means is operable to shut off the heater means independence on the exhaust gas temperature.

24. An internal combustion engine according to claim 23, furthercomprising means operable to shut off the flame-suction-air heater meansin dependence on the rotational speed.

25. An internal combustion engine according to claim 22, furthercomprising means operable to shut off the flame-suction-air heater meansin dependence on the rotational speed.

26. An internal combustion engine according to claim 15, characterizedby means for utilizing the heater means also for starting the engine.

27. An internal combustion engine according to claim 13, characterizedin that each piston of the engine is provided with heat-insulating meansfor preventing the heat flow from the piston top surface on the side ofthe combustion space to the piston sliding surfaces.

28. An internal combustion engine according to claim 27, characterizedin that said insulating means is formed by an annular groove in thepiston top.

' jection pump.

29. An internal combustion engine according to claim 17, characterizedby further means for shutting off the heater means upon reaching atemperature in the combustion space of the internal combustion enginewhich is sufficient for an ignition without preheating by the heatermeans.

30. An internal combustion engine according to 33. An internalcombustion engine according to claim 13, wherein said measuring meansmeasures the specific gravity of the fuel.

34. An internal combustion engine according to claim 30, characterizedby means for utilizing the flame-suction-air heater means also forstarting the enln. g 35. An internal combustion engine according toclaim 34, characterized in that each piston of the engine is providedwith heat-insulating means for preventing the heat flow from the pistontop surface on the side of the combustion space to the piston slidingsurfaces.

36. An internal combustion engine according to claim 35, characterizedin that said insulating means is formed by an annular groove in thepiston top.

37. An air-compressing, injection-type internal combustion engine withauto-ignition for multi-fuel operation, which comprises aflame-suction-air heater means, and means for setting into operation theflamesuction-air heater means during the operation of the engine underload with apoorly ignitable fuel, characterized by a means for measuringauxiliary magnitudes which indicate the ignitability of the internalcombustion engine fuel and which readies the operability of theflame-suction-air heater means only in the presence of poorly ignitablefuels.

38. An internal combustion engine according to claim 37, wherein saidmeasuring means measures the specific gravity of the fuel.

1. A method of operating an air-compressing and auto-igniting injectioninternal combustion engine with multiple fuel operating capabilitycomprising: providing a selectively operable flame-suction-air heatermeans for selectively heating intake air supplied to the engine, andcontrolling the operation of said heater means with control means,wherein said controlling includes measuring auxiliary magnitudes whichindicate the ignitability of fuel being supplied to the engine andoperating said heater means during at least some engine operatingconditions only when relatively poorly ignitable fuel is being suppliedto the engine.
 2. A method according to claim 1, characterized in thatthe poorly ignitable fuel is gasoline.
 3. A method according to claim 2,characterized in that the internal combustion engine has a relativelylow compression ratio.
 4. A method according to claim 1, comprising thestep of using the same fuel for the operation of the heater means as isused for the operation of the internal combustion engine.
 5. A methodaccording to claim 4, further comprising the step of automaticallyshutting off the heater means upon reaching a temperature in thecombustion space of the engine sufficient for an ignition withoutpreheating by the heater means.
 6. A method according to claim 1,further comprising the step of automatically shutting off the heatermeans upon reaching a temperature in the combustion space of the enginesufficient for an ignition without preheating by the heater means.
 7. Amethod according to claim 6, wherein said step of automatically shuttingoff the heater means includes detecting the quantity of fuel beingsupplied to the engine.
 8. A method according to claim 6, wherein saidstep of automatically shutting off the heater means includes detectingthe engine exhaust gas temperature.
 9. A method according to claim 1,wherein said controlling includes operation of said heater meansindependently of the fuel being supplied to the engine during enginestarting operations at low outside temperatures and maintainingoperation of said heater means after said engine starting operationsonly when said relatively poorly ignitable fuel is being supplied to theengine.
 10. A method according to claim 9, further comprising the stepof automatically shutting off the heater means upon reaching atemperature in the combustion space of the engine sufficient for anignition without preheating by the heater means.
 11. A method accordingto claim 1, wherein said measuring includes measuring the specificgravity of the fuel.
 12. A method according to claim 1, furthercomprising the step of automatically shutting off the heater means independence on the engine rotational speed.
 13. An internal combustionengine for multi-fuel operation comprising: heater means for heatingintake air being supplied to the engine, and heater control means forautomatically controlling the operation of said heater means, whereinsaid control means includes fuel characteristic measuring means formeasuring auxiliary magnitudes which indicate the ignitability of fuelbeing supplied to the engine and means for maintaining operation of saidheater means during at least some engine operating conditions only whenrelatively poorly ignitable fuel is detected by said fuel characteristicmeasuring means.
 14. An internal combustion engine according to claim13, wherein said control means includes means for operating said heatermeans independently of the ignitability of the fuel being supplied tothe engine during engine starting operations at low outside temperaturesand means for mAintaining operation of said heater means after thetermination of engine starting operations only when said relativelypoorly ignitable fuel is being supplied to the engine.
 15. An internalcombustion engine according to claim 13, wherein said engine is anair-compressing, injection-type engine with auto-ignition.
 16. Aninternal combustion engine according to claim 15, characterized in thatthe engine has a relatively low compression ratio for auto-ignitingmulti-fuel operation.
 17. An internal combustion engine according toclaim 15, characterized in that the compression ratio of the engine isof the order of the compression ratio utilized in customary Dieselengines.
 18. An internal combustion engine according to claim 17,characterized in that the fuel which is poorly ignitable is gasoline.19. An internal combustion engine according to claim 15, characterizedby means for supplying the same fuel for the operation of the heatermeans as is used for the operation of the internal combustion engine.20. An internal combustion engine according to claim 15, characterizedby further means for shutting off the heater means upon reaching atemperature in the combustion space of the internal combustion enginewhich is sufficient for an ignition without preheating by the heatermeans.
 21. An internal combustion engine according to claim 20, whereinsaid further means shuts off the heater means as a function of thequantity of fuel injected into the internal combustion engine.
 22. Aninternal combustion engine with an injection pump having a control rackaccording to claim 21, characterized in that said further means isoperable as a function of the position of the control rack of theinjection pump.
 23. An internal combustion engine according to claim 20,characterized in that said further means is operable to shut off theheater means in dependence on the exhaust gas temperature.
 24. Aninternal combustion engine according to claim 23, further comprisingmeans operable to shut off the flame-suction-air heater means independence on the rotational speed.
 25. An internal combustion engineaccording to claim 22, further comprising means operable to shut off theflame-suction-air heater means in dependence on the rotational speed.26. An internal combustion engine according to claim 15, characterizedby means for utilizing the heater means also for starting the engine.27. An internal combustion engine according to claim 13, characterizedin that each piston of the engine is provided with heat-insulating meansfor preventing the heat flow from the piston top surface on the side ofthe combustion space to the piston sliding surfaces.
 28. An internalcombustion engine according to claim 27, characterized in that saidinsulating means is formed by an annular groove in the piston top. 29.An internal combustion engine according to claim 17, characterized byfurther means for shutting off the heater means upon reaching atemperature in the combustion space of the internal combustion enginewhich is sufficient for an ignition without preheating by the heatermeans.
 30. An internal combustion engine according to claim 29, furthercomprising means operable to shut off the heater means in dependence onthe rotational speed.
 31. An internal combustion engine according toclaim 30, wherein said further means shuts off the heater means as afunction of the quantity of fuel injected into the internal combustionengine.
 32. An internal combustion engine with an injection pump havinga control rack according to claim 31, characterized in that said furthermeans is operable as a function of the position of the control rack ofthe injection pump.
 33. An internal combustion engine according to claim13, wherein said measuring means measures the specific gravity of thefuel.
 34. An internal combustion engine according to claim 30,characterized by means for utilizing the flame-suction-air heater meansalso for starting the engine.
 35. An internal combustion engineaccording to claim 34, characterized in that each piston of the engineis provided with heat-insulating means for preventing the heat flow fromthe piston top surface on the side of the combustion space to the pistonsliding surfaces.
 36. An internal combustion engine according to claim35, characterized in that said insulating means is formed by an annulargroove in the piston top.
 37. An air-compressing, injection-typeinternal combustion engine with auto-ignition for multi-fuel operation,which comprises a flame-suction-air heater means, and means for settinginto operation the flame-suction-air heater means during the operationof the engine under load with a poorly ignitable fuel, characterized bya means for measuring auxiliary magnitudes which indicate theignitability of the internal combustion engine fuel and which readiesthe operability of the flame-suction-air heater means only in thepresence of poorly ignitable fuels.
 38. An internal combustion engineaccording to claim 37, wherein said measuring means measures thespecific gravity of the fuel.